It is known to use interconnects arranged in one plane to rewire the contact surfaces (contact pads) of the component into connection contacts, which are preferably arranged in grid form on the surface of the component. These are also designed as contact surfaces in various applications and with the aid of which the component is integrated into an electronic circuit. These arrangements are becoming increasingly important for wafer-level packages or chip-size packages that are produced while still part of the wafer and are all simultaneously provided with rewiring, protective passivation (BCB) and connection contacts before being divided up for the standard subsequent mounting processes. To satisfy the constant demand for ever smaller component dimensions, these components are not encapsulated in a housing, but rather at most have protective passivation or plastic layers, so that their dimensions completely or virtually correspond to those of the integrated circuit (chip) obtained.
There is substantially no separate protection for the interconnects. However, since reliability tests, for example the highly accelerated stress test (HAST), show the interconnects to have signs of corrosion, a second mask, which is to be produced after removal of the first mask and is used to surround the copper interconnect, which serves as the actual electrical conductor, with a nickel-gold layer, has been designed. The nickel-gold layer comprises an individual layer of nickel and an individual layer of gold and is preferably applied by sputtering.
However, it has been determined that the copper core of the interconnects, at its flanks, on account of the shape of the flanks of the openings in the first mask, forms an overhang region in which a residue of the positive resist remains after the latter has been developed, and that this residue of resist can in turn cause corrosion or contamination of the component.
A further possible option for protecting the interconnects consists in applying a passivating layer made from dielectric material over the entire component. However, this thin covering over the entire surface is not suitable for components which have a three-dimensional structure in terms of objects projecting above the component surface. Examples of objects of this type include resilient elevations (elastomer bumps), which carry the connection contacts of the component and are used for reliable contact-connection when connecting materials with significantly different expansion coefficients.
Since the material which forms the covering often flows off these elevations, but the interconnects may also cover these elevations, and furthermore the connection contacts are constructed, similarly to the interconnects, on the top of the elevations and therefore have the same problems, this form of protection cannot be used.